This is my guide for Not So Vast Forest
You will need 4 points in the third tree. You need all 3 life skills, so you will haev 9 lives. any extra points go into the warrior tree. (first tier, and for second tier it's poison and energy.)
Place a warrior at each U turn, and one behind that (Here's a map to show what I mean.
O = path
W = warrior
OOO
OWO
OWO
for both U turns. upgrade them like this - Poison, Consecrate, Generalism, Tactician (it's the damage dealer, and I only had 4 skill points anyway and they went in the third tree). Go for damage. When necessary, fill all the other tiles, and have a mix of poison and energy. I think I had a couple of mages, too. This should kill the enemies before they take all 9 of your lives. ((it's almost impossible to stop them leaking, that's why the life skills ARE VITAL. The 4th point went on Frugal, if that's of any help to you.)